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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        var num = 10;
        // num = num+1    num++
        // num = num + 2 // num+=2
        num += 2;
        console.log(num);
        // kankan
        // 还有+= -= *= /=
    </script>
</body>

</html>